Method for producing a press-quenched component, and press mold

ABSTRACT

The present disclosure relates to a method for producing a press-quenched component from a hot-formable steel sheet blank, in which, in a first step, the blank is heated to a temperature of approximately 900° C. and, in a second step, the blank is arranged in a press mold and formed, wherein a drawing bead is created on the blank and the region of the press mold in which the drawing bead is arranged is heated prior to introduction of the blank into the press mold. The present disclosure also relates to a press mold for the above method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of German Application Number 102017201674.4 filed on Feb. 2, 2017. The disclosure of the above application is incorporated herein by reference.

FIELD

The present disclosure relates to a method for producing a press-quenched component from a hot-formable steel sheet blank. The present disclosure also relates to a press mold for a method for producing a press-quenched component.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

In order to satisfy the high requirements for components, in particular automotive body parts, with respect to stiffness and strength, these components are made of high-strength to ultra high-strength steel construction materials. The components are often produced in a hot-forming process in which a blank is first cut from a coil. This blank is heated to a temperature at which the material structure is in the austenitic phase. After heating, the blank is arranged in a press mold which brings the blank into the desired component shape. The formed component is cooled while being held mechanically, tempering or quenching the component. Various modifications of the above-described hot-forming process are known.

EP 1 536 898 B1 discloses a method for producing a metallic formed component, in particular a body part, from a blank made of an unquenched hot-formable steel sheet. First, the blank is worked using a cold-working method, in particular by deep drawing, to produce a component preform (process step II). Then, the edges of the component preform are trimmed to a rim contour that approximately corresponds to the component that is to be produced (process step III). Finally, the trimmed component preform is heated and is press-quenched in a hot-working tool (process step IV). The component produced in this manner already has the desired rim contour after hot-working, so that final trimming of the component rim is not necessary.

EP 1 646 459 A1 and U.S. Pat. No. 8,127,449 B2 described, for example, a method for producing press-quenched components of a body part, made from hot-workable steel sheet blanks, in which, in a first step, a component preform is formed by cold- or hot-working from the blank that has previously been coated with a first layer. In a second step, the component preform is heated and press-quenched in a hot-working tool. In a subsequent step, the press-quenched component preform is covered with a second corrosion-protection layer.

DE 10 2013 013 270 A1 discloses a method and a device for producing a press-quenched component from a blank, in which, during the process step, both the blank and the component that is to be formed from the blank are each continuously checked by means of sensors in order to obtain state variables that can be assigned to the blank and to the component that is to be formed, wherein the state variables obtained by means of sensors are subjected to tolerance-imposed evaluation in which, in the event of at least one state variable detected during a certain process step exceeding a predefined tolerance, an open- or closed-loop control signal is generated, which influences at least one process parameter characterizing at least the process step in question.

U.S. Pat. No. 9,340,233 B2 discloses a method for producing a hot-worked and press-quenched metal component for a motor vehicle, in which the metal component obtains at least two regions with different hardnesses. The method comprises the following method features: providing a quenchable sheet metal blank which is heated to at least austenizing temperature, intermediate cooling of a first region of the sheet metal blank, the rate of cooling being chosen to be greater than the lower critical cooling rate of the material of the sheet metal blank, and hot-forming and press-quenching of the sheet metal blank in a press-quenching tool to give the metal component.

U.S. Patent Publication No. 2016/0010169 A1 proposes a method for hot-working, in particular for press-quenching a component, wherein in a localized region of the component a reduced martensite hardness is generated by localized reduction of a press pressure exerted on a surface of the component.

JP 2003/328031 A2 discloses a method for press-quenching a component in a press mold consisting of two mold parts which, in the closed state, have mutually opposite depressions. The heated component is arranged in the press mold and cooled. The depressions give rise to different cooling rates in those regions in which the component is in contact with the press mold, and in those regions in which the component is arranged in the region of the depression.

U.S. Pat. No. 7,513,137 B2 describes a method for hot-forming workpieces from a steel blank, in which, prior to or during the hot-forming, an impression is introduced into cutting zones in the workpiece, which reduces the wall thickness in the cutting zone. After hot-forming, a cut is created in the quenched component, within the impression.

According to U.S. Patent Publication No. 2011/0232806 A2, a stringer is produced by hot-working and press-quenching a steel sheet blank, with at least one region that is partially heat-treated after press-quenching, wherein a transition region of breadth less than or equal to 50 mm is formed between the heat-treated region and the non-heat-treated region.

Another method for producing a motor vehicle component having at least one hot-formed and press-quenched component made of high-strength steel is known from U.S. Pat. No. 9,057,114 B2. According to that document, the motor-vehicle component is used as a structural component and/or a safety component for a motor vehicle, with the following method steps: partial heat-treatment of the automotive component in regions, the regions being first heated to a heat-up temperature (T1) in a temperature range between 500° C. and 900° C.; maintaining the heat-up temperature (T1) for a residence time (t2); and cooling from the heat-up temperature (T1) in at least one phase.

A drawback of the above-described method is that it cannot be used to work blanks having drawing beads or drawing strips. Drawing beads are generally used in “cold” pressing methods in order to control the material flow and avoid irregularities. A method that describes the use of drawing beads is for example described in U.S. Pat. No. 7,748,743 B2. According to the known method, a blank is worked in a press tool. A drawing bead is formed in the blank, at least at one rim at a distance from the outer edge of the blank. The drawing bead serves as a material reserve during the working process. Then, the blank is worked in the press tool to give the structural component or chassis component. In this context, in the press tool, the drawing bead is smoothed by displacement of material in the direction of the outer edge, and the rim is pressed against a counter-bearing in the press tool, whereby the rim is worked into a recess in the press tool, resulting in a bead at the rim.

It has been found that the provision of a drawing bead is not possible in the context of press-quenching, since the material flow of the drawing bead cannot be controlled as in the known “cold” press methods owing to the rapid temperature change by contact between the heated blank and the cold press mold during press-quenching.

SUMMARY

Since the range of possible geometries is limited in comparison to the “cold” press methods, owing to the fact that drawing beads cannot be used during press-quenching, the present disclosure provides a method for press-quenching which is also suitable for the use of drawing beads. The present disclosure also provides a press mold that is suitable for carrying out the method.

It is pointed out that the features and measures specified individually in the following description may be combined with one another in any desired technically meaningful way and discloses further refinements of the present disclosure. The description, in particular in conjunction with the figures, characterizes and specifies the present disclosure further.

In a first step of the proposed method for producing a press-quenched component from a hot-formable steel sheet blank, the blank is heated to a temperature of approximately 900° C. In a second step, the blank is arranged in a press mold and formed. According to the present disclosure, it is provided that a drawing bead is created on the blank and the region of the press mold in which the drawing bead is arranged is heated prior to introduction of the blank into the press mold.

In the case of the present disclosure, it has been recognized that it is also possible to produce blanks having a drawing bead by press-quenching if that region of the blank having a drawing bead is not subjected to abrupt cooling in the press mold. Abrupt cooling is avoided if that region of the press mold in which the drawing bead is arranged is heated prior to arranging. By virtue of the heating of the region, and thus the absence of abrupt cooling, the component does develop less martensitic properties in this region, but this has the advantage that the structure in this part of the component remains such that the material flow can take place unhindered. This makes it possible for sufficient retention forces to be applied during the pressing procedure in order to avoid irregularities in the component.

According to one form of the method according to the present disclosure, the region in which the drawing bead is arranged is heated to a temperature of at least 400° C. It has been found that, above this temperature, the component possesses good formability in the region of the drawing bead. Accordingly, it is also advantageous to control the temperature of the region in which the drawing bead is arranged such that it does not drop below 400° C.

Another form of the method according to the present disclosure provides that the temperature of the heated region in which the drawing bead is arranged is set according to the geometry of the component.

Advantageously, according to one form of the present disclosure, boron steel is used to make the blank. The use of boron steel permits weight-reduced possibilities in the structure of the components without having to make excessive compromises in the design. It is however also conceivable to combine the method with Tailor Welded Blanks (TWB), Tailor Rolled Blanks (TRB) and/or Tailor Tempered Blanks (TTB) as blanks.

The present disclosure provides a press mold for producing a press-quenched component from a hot-formable steel sheet blank, in which, in a first step, the blank is heated to a temperature of approximately 900° C. and, in a second step, the blank is arranged in a press mold and formed. The present disclosure provides that the press mold is divided into at least two segments, wherein at least one segment can be heated.

It is expedient if the press mold has at least three segments, of which two can be heated. In that context, the heatable segments are expediently arranged in the region of the drawing bead, that is to say near the rim.

According to one form of the press mold according to the present disclosure, thermal insulation is arranged between the heatable segment and the other segment. This provides the advantage of avoiding an exchange of heat between the two segments.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a three-dimensional schematic illustration of an exemplary form of a press mold according to the present disclosure; and

FIG. 2 is a schematic illustration of a blank having a drawing bead, introduced into the press mold shown in FIG. 1.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

FIG. 1 and FIG. 2 shows an exemplary form of a press mold 1 according to the present disclosure. The press mold 1 comprises a die 2 and three punches 3, 3′, wherein the die 2 has recesses 4 that are designed and arranged such that they form the counterpart to the punches 3 during the press-quenching procedure. The press mold 1 comprises three segments 5, 6 and 7, wherein segments 5 and 7 are in heated regions 5′, 7′ of the press mold 1, and segment 6 is arranged in a cooled region 6′.

In order to produce the component, the heated blank 8 is arranged between the die 2 and the punches 3, 3′. Then, the die 2 and the punches 3, 3′ are brought together so that the blank 8 is formed into the desired component by the punches 3, 3′ pushing into the recesses 4 of the die 2. Arranging the segments 5, 6, 7 in different temperature regions means that the microstructure in the blank changes unevenly. Thus, in the cooled region 6′ the blank 8 experiences quenching due to the rapid cooling. In the heated region 5′, 7′, there is no abrupt cooling since in this region the segments 5 and 7 are heated by the heated region. The consequence of this is that those regions of the component that are arranged in the heated region 5′, 7′ do not have the same martensitic properties as the quenched region of the component. This makes it possible for a drawing bead 9 to be arranged in the respective heated region 5′, 7′, since in this region the material flow during the pressing procedure is better than in the cooled region, and the drawing bead 9 makes it possible to even out irregularities. Thus, the present disclosure makes it possible to use the advantages of the drawing bead even in the context of press-quenching.

The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure. 

What is claimed is:
 1. A method for producing a press-quenched component from a hot-formable steel sheet blank, the method comprising: heating the blank to a temperature of about 900° C.; arranging the blank in a press mold; and forming the blank, wherein a drawing bead is created on the blank and a region of the press mold where the drawing bead is arranged is heated prior to introduction of the blank into the press mold.
 2. The method as claimed in claim 1, wherein the heated region in which the drawing bead is arranged is heated to a temperature of at least 400° C.
 3. The method as claimed in claim 1, wherein a temperature of the heated region in which the drawing bead is arranged is controlled such that it does not drop below 400° C.
 4. The method as claimed in claim 1, wherein a temperature of the heated region in which the drawing bead is arranged is set according to a geometry of the component.
 5. The method as claimed in claim 1, wherein boron steel is used to make the blank.
 6. The method as claimed in claim 1, wherein the blank is at least one of Tailor Welded Blanks (TWB), Tailor Rolled Blanks (TRB) and Tailor Tempered Blanks (TTB).
 7. The method as claimed in claim 1, wherein the press mold is divided into at least two segments.
 8. The method as claimed in claim 7, wherein at least one segment of the at least two segments is heated.
 9. The method as claimed in claim 8, wherein thermal insulation is arranged between the heated segment and the other segment.
 10. The method as claimed in claim 1, wherein the press mold includes at least three segments.
 11. The method as claimed in claim 10, wherein two of the at least three segments is heated.
 12. The method as claimed in claim 11, wherein the drawing beads are arranged in the two heated segments.
 13. The method as claimed in claim 11, wherein thermal insulation is arranged between the heated segments and the non-heated segment.
 14. A component manufactured according to the method of claim
 1. 15. A press mold comprising: at least two segments; a die defining at least two recesses and arranged in the at least two segments; and punches, wherein a blank having at least one drawing bead is arranged between the die and the punches and each recess receives a punch when the die and punches are pressed together.
 16. The press mold as claimed in claim 15, wherein at least one of the at least two segments is heated and the at least one drawing bead is arranged in the heated segment.
 17. The press mold as claimed in claim 16, wherein a temperature of the heated segment is at least 400° C.
 18. The press mold as claimed in claim 15, wherein the number of segments is three and two of the three segments is heated.
 19. The press mold as claimed in claim 18 further comprising thermal insulation arranged between the two heated segments and non-heated segment.
 20. The press mold as claimed in claim 18, wherein the drawing beads are arranged in the heated segments. 